Radio communicating system, radio communicating method, radio station, control station and program

ABSTRACT

A radio station communicates control information for multipoint cooperating communication, in which a plurality of radio stations takes part in data transmission/reception of a terminal, with another radio station taking part in the multipoint cooperating communication and/or a control station that manages the radio station.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. application Ser. No.13/389,401 filed Feb. 7, 2012, which is a National Stage Entry ofInternational Application PCT/JP2010/063407 filed Aug. 6, 2010, whichasserts priority rights based on JP Patent Application 2009-184996 filedon Aug. 7, 2009. The entire contents of disclosure of the PatentApplication of the senior filing date are to be incorporated byreference into the present Application.

TECHNICAL FIELD

This invention relates to a radio communicating technique. Moreparticularly, it relates to a system that may be applied to advantage toa radio communication system in which a plurality of radio base stationsmay have communication simultaneously with a terminal.

BACKGROUND

In 3GPP LTE (3rd Generation Partnership Project Long Term Evolution), asone of the next-generation cellular systems, investigations into SON(Self Organizing Network) are going on from the perspective of reducingthe operation expenditure (OPEX).

SON has such functions as

-   -   self-configuration;    -   self-optimization; and    -   self-healing.        Techniques for achieving the different objectives are being        considered (Non-Patent Documents 1 and 2).

In Non-Patent Document 2, as one of SON techniques there is listed radioparameter optimization with a view to accomplish respective objectives,such as maximizing the throughput, minimizing the delay or maximizingthe coverage.

Examples of radio parameters include the transmission power of a radiobase station (sometimes abbreviated to a ‘base station’), an antennatilt angle of a base station, neighbor cell information and handoverparameters. One or more of these radio parameters are changed asnecessary to accomplish the above objectives.

In the following, attention is focused on the neighbor cell information,out of the above radio parameters, which is related to the presentinvention.

In LTE, there is stipulated an ANR (Automatic Neighbor Relation)function as one of methods for optimizing the neighbor cell list(Non-Patent Document 1). This ANR function renders it possible toautomatically add a cell (not a target for a measurement report) that isnot recognized by a base station of a serving cell to a neighbor celllist. The following describes the ANR function that generates a neighborcell list of the same frequency in the LTE system, as an example, withreference to FIG. 18.

In FIG. 18, it is assumed that a terminal (UE: user equipment) is in acell1 and communicates with a base station 1 (eNB1), and that a cell2 isadjacent to the cell1.

It is assumed that the presence of an eNB2 (cell2) is not recognized bythe eNB1.

The UE detects that a received power of a down-link reference signal(pilot signal) received from the cell2 is greater than or equal to agiven threshold value ((Measurement (Phy CID=5) <step 0>. The UEnotifies the eNB1 of the physical cell ID of the cell2 (Physical CellID: Phy CID=5) and the received power value with a measurement report(Measurement report) <step 1>.

Since the eNB1 is informed by this report of the presence of Phy CID(=5) the eNB1 does not recognize, the eNB1 requests a global cell ID(Global CID) from the UE as the further information regarding therelevant cell (Report Global CID request) <step 2>.

The UE reads the broadcast information of the cell2 broadcasted over BCH(Broadcast CHannel), detects the Global CID of the cell2 (=19) <step 3>,and makes a report to the eNB1 (Report Global CID=19) <step 4>.

The eNB1 then establishes connection with the eNB2 (X2 setup) andexchanges with the eNB2 information such as served cell lists (Servedcell lists) mutually. X2 is a logical connection (interface) betweeneNB's.

The information necessary for optimizing the neighbor cell list may thusbe obtained. The base station determines whether or not to add the newcell to the neighbor cell list, depending on whether or not the value ofthe received power of the downlink signal of another cell reported by aterminal is greater than or equal to a given threshold value and whetheror not the number of times of the report exceeds a given number (PatentDocument 1).

FIG. 19 is a diagram illustrating the ANR function of the eNB and theNRT (see Non-Patent Document 1). Specifically, FIG. 19 shows an exampleof a neighbor cell list retained by an eNB. The neighbor cell listincludes an index, identifier of a target cell (Target Cell ID: TCI),associated with the index, and attributes for each of the target cells(“No Remove”, “No HO” and “No X2”). It is noted that HO means Hand Overand X2 means an interface between base stations in LTE. Such neighborcell list is termed a neighbor relation table (NRT). The NRT, a neighborcell list including an index, an identifier of a target cell associatedwith the index (TCIs) and attributes of each target cell, as one entry,is used as part of the ANR (Automatic Neighbor Relation) function. Incase a check (check mark) is inserted in “No Remove”, a radio basestation never deletes the cell from the neighbor cell list (deleteinhibited). In case a check is inserted in “No HO”, the radio basestation does not use the cell in question as an object in the hand-over(use inhibited). In case a check is inserted in “No X2”, X2 is not used(is not to be used) to perform specific procedures for the base stationthat manages the cell.

Not only the large improvement of peak throughput compared with WCDMA(Wideband Code Division Multiple Access) but also a method of improvingcell edge throughput are investigated for the LTE. One of theinvestigations is ICIC (Inter Cell Interference Coordination).

The ICIC is a technique of exchanging information on the neighbor cells,for example, resource usage ratio and traffic load status, between thebase stations, to control the radio resources, so as to reduce aneighbor cell interference. The ICIC may be said to be SON in the broadsense of the term (Non-Patent Document 1).

The investigation of LTE Advanced, in which the LTE is further advanced,is also commenced, and investigation of CoMP transmission/reception(Coordinated MultiPoint transmission and reception) is being conductedas a means for further improving the cell edge throughput.

The CoMP is a technique in which a plurality of base stationssimultaneously sends down-link data to a specified terminal orsimultaneously receives uplink data from a specified terminal(Non-Patent Document 3).

As regards the CoMP, a serving cell (Serving Cell), a cooperating set(CoMP cooperating set) and so forth are defined.

The serving cell is a cell that transmits control information to aterminal over a down-link control channel (PDCCH).

The cooperating set (CoMP cooperating set) is a set of cells thatdirectly or indirectly take part in transmitting data to a terminal overthe down-link control channel (Physical Down Link Shared CHannel orPDSCH).

[NON-PATENT DOCUMENTS]

-   [Non-Patent Document 1] 3GPP TS36.300 v880 (Internet <URL>    http://www.3gpp.org/ftp/Specs/html-info/36300.htm)-   [Non-Patent Document 2] NGMN technical documents: Use Cases Related    to Self Organizing Networks (Internet <URL>    http://www.ngmn.org/uploads/media/NGMN_Use_Cases_Self_Organizing_Network_2_2.02.pdf)-   [Non-Patent Document 3] 3GPP TR.36.814 v121 (Internet <URL>    http://list.etsi.org/scripts/wa.exe.?A2=ind0907&L=3gpp_tsg_ran_wgl&T=0&O=A&P=6822    [PATENT DOCUMENT]-   [Patent Document 1] JP Patent Kohyo Publication No. JP-P2000-505251A

SUMMARY

The entire contents disclosed in the Non-Patent Documents 1 to 3 and thePatent Document 1 is to be incorporated by reference into the presentApplication.

The following is an analysis of the related technique by the presentinvention.

To implement CoMP transmission/reception, it is necessary toappropriately configure a relation of a plurality of neighbor cellstaking part in the CoMP transmission/reception, that is, toappropriately configure the cooperating set (CoMP cooperating set).

Moreover, to reduce OPEX (operational expenditure), it is necessary toconfigure automatically the cooperating set (CoMP cooperating set). Thisis the information obtained by the present inventor.

As a method to accomplish the above desideratum, the present inventorconducted eager researches into whether or not it is possible toautomatically generate a cooperating set (CoMP cooperating set) bymaking use of the self-optimization method of the neighbor cell list(NRT) shown e.g., in FIG. 19. In this case, it is highly likely that, inanother cell where the received power is high, or in a base station thatmanages such a cell, the CoMP transmitting/receiving function is notsupported. Alternately, it may be expected that, even if, in anothercell where the received power is high (or in a base station managingsuch cell), CoMP transmission/reception is supported, thetransmission/reception scheme that is usable (for example, thecoordinated scheduling, coordinated beam forming, joint processing,joint transmission or the like) is different. It is therefore crucialthat a cooperating set (CoMP cooperating set) will be automaticallygenerated in such a manner as not to add to the set a cell that is notin support of CoMP and/or a cell that is unable to execute CoMPtransmission/reception (results of study by the present inventor).

It is therefore an object of the present invention to provide a systemand a method for automatically generating a cooperating set (CoMPcooperating set) which is a set of radio stations taking part inmultipoint cooperating communication or a set of cells of such radiostations, in such a manner as not to add to the set a cell that is notin support of CoMP and/or a cell that is unable to execute CoMPtransmission/reception.

To accomplish the above object, the present invention provides a radiocommunication system, a radio communication method, a radio basestation, a control station and a program that use following means.

According to the present invention, there is provided a radiocommunication system wherein a radio station communicates controlinformation regarding multipoint cooperating communication, in which aplurality of radio stations take part in data transmission/receptionwith a terminal, with another radio station taking part in themultipoint cooperating communication and/or with a control stationmanaging the radio station.

According to the present invention, there is also provided a radiocommunication method comprising:

a radio station communicating control information regarding multipointcooperating communication, in which a plurality of radio stations takepart in data transmission/reception with a terminal, with another radiostation taking part in the multipoint cooperating communication and/orwith a control station managing the radio station.

According to the present invention, there is also provided a radiostation radio station communicating control information regardingmultipoint cooperating communication, in which a plurality of radiostations take part in data transmission/reception with a terminal, withanother radio station taking part in the multipoint cooperatingcommunication and/or with a control station managing the radio station.

According to the present invention, there is also provided a controlstation communicating control information regarding multipointcooperating communication, in which a plurality of radio stations takepart in data transmission/reception with a terminal, with one radiostation of the plurality of radio stations and/or with another radiostation taking part in the multipoint cooperating communication with theone radio station.

According to the present invention, there is also provided a programcausing a computer composing a radio station to execute the processingcomprising:

communicating control information regarding multipoint cooperatingcommunication, in which a plurality of radio stations take part in datatransmission/reception with a terminal, with another radio stationtaking part in the multipoint cooperating communication and/or with acontrol station managing the radio station.

According to the present invention, there is also provided a programcausing a computer composing a control station to execute the processingcomprising:

communicating control information regarding multipoint cooperatingcommunication, in which a plurality of radio stations take part in datatransmission/reception with a terminal, with one radio station of the aplurality of radio stations and/or with another radio station takingpart in the multipoint cooperating communication with the one radiostation.

According to the present invention, a cooperating set, which is a set ofradio stations taking part in multipoint cooperating communication or aset of cells of such radio stations, may automatically be generated inconsideration of the presence/absence of the multipoint cooperatingcommunication function in each radio station or the multipointcommunication system each radio station is in support of.

Still other features and advantages of the present invention will becomereadily apparent to those skilled in this art from the followingdetailed description in conjunction with the accompanying drawingswherein only exemplary embodiments of the invention are shown anddescribed, simply by way of illustration of the best mode contemplatedof carrying out this invention. As will be realized, the invention iscapable of other and different embodiments, and its several details arecapable of modifications in various obvious respects, all withoutdeparting from the invention. Accordingly, the drawing and descriptionare to be regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a configuration of a radio communicationsystem according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram showing another cell configuration of a radiocommunication system according to an exemplary embodiment of the presentinvention.

FIG. 3 is a sequence diagram for illustrating a method for configuring acooperating set (CoMP cooperating set) according to a first exemplaryembodiment of the present invention.

FIG. 4 is a diagram illustrating timer control in the configuration ofthe cooperating set (CoMP cooperating set) according to the firstexemplary embodiment of the present invention.

FIG. 5 is another sequence diagram for illustrating a method forconfiguring a cooperating set (CoMP cooperating set) according to thefirst exemplary embodiment of the present invention.

FIG. 6 is yet another sequence diagram for illustrating a method forconfiguring a cooperating set (CoMP cooperating set) according to thefirst exemplary embodiment of the present invention.

FIG. 7 is a diagram showing an example of a neighbor cell list ofrelated arts.

FIG. 8 is a diagram showing an example of a neighbor cell list accordingto the present invention.

FIG. 9 is a diagram showing another example of a neighbor cell listaccording to the present invention.

FIG. 10 is a diagram showing an example of a cooperating set (CoMPcooperating set) according to the present invention.

FIG. 11 is a diagram showing another example of a cooperating set (CoMPcooperating set) according to the present invention.

FIG. 12 is a block diagram showing a configuration of a radio basestation (eNB) according to the present invention.

FIG. 13 is a block diagram showing a configuration of a control station(O&M) according to the present invention.

FIG. 14 is a sequence diagram for illustrating a method for configuringa cooperating set (CoMP cooperating set) according to a modification ofthe first exemplary embodiment of the present invention.

FIG. 15 is a sequence diagram for illustrating a method for configuringa cooperating set (CoMP cooperating set) according to a second exemplaryembodiment of the present invention.

FIG. 16 is a sequence diagram for illustrating a method for configuringa cooperating set (CoMP cooperating set) according to a third exemplaryembodiment of the present invention.

FIG. 17 is a sequence diagram for illustrating a method for configuringa cooperating set (CoMP cooperating set) according to a fourth exemplaryembodiment of the present invention.

FIG. 18 is a diagram for illustrating an ANR function.

FIG. 19 is a diagram for illustrating the NRT and the ANR function.

FIGS. 20A and 20B are diagrams for illustrating an example of a changeof a CoMP cell list.

FIG. 21 is a diagram for illustrating the CoMP of eNBs.

FIGS. 22A to 22C are diagrams for illustrating the CoMP of relay nodes.

PREFERRED MODES

The present invention will now be described in detail. Initially, as apremise of the present invention, issues that may arise in automaticallygenerating the cooperating set by making an adaptive use of theself-optimization of the neighbor cell list will be described.

A base station has a terminal in an own cell measure a received power ofa downlink signal of a neighbor cell and report information on theneighbor cell, such as Phy CID, and a measured value.

The base station then adds to the cooperating set a cell whose value ofthe received power reported exceeds a given threshold value and whosenumber of times of reports exceeds a given number.

By so doing, the cell that is capable of CoMP may appropriately beselected to enable improvement in the cell edge throughput as expected.

The above method may be said to be an appropriate method for generatingthe cooperating set, in which the throughput may be expected to beimproved insofar as the received power at the terminal is concerned.However, there may be cases where the method is not appropriate. Thatis, there may be a case where the CoMP transmission/reception functionis not always supported in another cell with strong received power (or abase station managing such another cell). In addition, there may be acase where, even if the CoMP transmission/reception is supported in theother cell with strong received power (or a base station managing suchother cell), the transmission/reception scheme usable in such other celldiffers.

According to the present invention, the base station (radio station)communicates control information regarding multipoint cooperatingcommunication with at least one other base station taking part in themultipoint cooperating communication in which a plurality of basestations take part in data transmission/reception with a singleterminal.

According to the present invention, the control information regardingmultipoint cooperating communication is the information configured orretained in one or more of the multiple radio stations.

According to the present invention, one of the radio stations, to whichbelongs the one terminal, may communicate the control informationregarding multipoint cooperating communication with another radiostation.

According to the present invention, the control information regardingmultipoint cooperating communication may include at least one offunctional information of the multipoint cooperating communication, theconfiguration information of the cooperating set and the access stratum(AS) configuration information.

According to the present invention, the radio station or the controlstation managing the radio station, may configure the cooperating set inaccordance with the control information regarding the multipointcooperating communication, the cooperating set which is a set of theradio stations directly or indirectly taking part in the multipointcooperating communication or a set of cells of such radio stations.

According to the present invention, the above mentioned multiple radiostations have the above mentioned multipoint cooperatingtransmission/reception function and control information regarding themultipoint cooperating communication may be communicated between one ofthe radio stations to which the one terminal belongs and which belongsto a cooperating set and neighbor radio stations, between the one radiostation and a control station, or between the neighbor radio station andthe control station, where the cooperating set is defined as a set ofthe radio stations taking part in the above mentioned multipointcooperating communication or a set of cells of such radio stations.

According to the present invention, the control information regardingthe multipoint cooperating communication may be communicated via thecontrol station between the above mentioned one radio station and theneighbor radio station.

According to the present invention, the functional information mayinclude information on at least one of presence/absence of themultipoint cooperating communication function and thetransmission/reception scheme of the multipoint cooperatingcommunication being supported.

According to the present invention, the configuration information mayinclude an identifier of the cooperating set.

According to the present invention, the access stratum configurationinformation may include at least one of radio resource managementinformation, terminal measurement configuration information andscheduler information.

According to the present invention, the terminal measurementconfiguration information may include at least one of a type (or sort)of the measurement information measured by the terminal, a period ofreporting the measurement information and the event information allowingthe terminal to decide whether or not the terminal is to make a reporton the measurement information.

According to the present invention, a trigger for communicating thecontrol information regarding the multipoint cooperating communicationmay include at least one of

information reported by the terminal satisfying a given condition,

establishing connection to the other radio station being about to beestablished or having already been newly done,

connection to the other radio station being about to be updated orhaving already been updated,

the control information having been requested from the other radiostation,

the control information having been requested from a radio station towhich belongs the one terminal, and

the control information having been requested from the control station.

According to the present invention, the above mentioned trigger mayinclude satisfying the condition that the received quality of a neighborcell reported by the terminal exceeds a given threshold value.

According to the present invention, a neighbor cell list indicating therelation between neighbor cells retained by the radio station and/or acontrol station (control station), may include, as one of attributesthereof, an attribute regarding the multipoint cooperatingcommunication. According to the present invention, the attributeregarding the multipoint cooperating communication may include

a flag indicating whether or not a neighbor cell belongs to the samecooperating set, and

an identifier of the cooperating set to which belongs the neighbor cell.

According to the present invention, the radio station and/or the controlstation may correlate the attribute regarding the multipoint cooperatingtransmission/reception and the scheduler information to each other.

According to the present invention, in automated generation of thecooperating set, the cooperating set (CoMP cooperating set) isautomatically generated in a manner so as not to add a cell notsupporting the CoMP and/or a cell unable to execute CoMPtransmission/reception to the set.

In the description to follow, it is supposed that the radiocommunication system is 3GPP LTE.

In the description to follow, CoMP (Coordinated Multipoint)transmission/reception is used as an example of the ‘multipointcooperating communication’ by a plurality of base stations. The ‘CoMPcooperating set’ is used as an example of the ‘cooperating set’ which isa set of cells of radio base stations taking part directly or indirectlyin the cooperating transmission/reception (Non-Patent Document 3).

<Configuration of First Wireless Communication System>

FIG. 1 is a diagram schematically illustrating an example of theconfiguration of a radio communication system according to an exemplaryembodiment of the present invention. This radio communication systemincludes radio base stations (eNB: evolved Node B or E-UTRAN Node B(E-UTRAN: Evolved UTRAN)) eNB1, eNB2 and eNB3.

The radio communication system also includes an O&M (Operation &Maintenance Server), also termed OMC (Operation and Maintenance Center),and radio terminals (UEs) UE1 and UE2.

It is assumed that the radio base stations eNB1, eNB2 and eNB3 manage acell1 (Cell 1), a cell2 (Cell 2) and a cell3 (Cell 3), respectively. Itis also assumed that, in the example shown in FIG. 1, the UE1 and theUE2 both stay in the cell1. It is noted that if the radio base stationseNB1, eNB2 and eNB3 manage a plurality of each of the sub-divided cellscell1-1 to cell1-3, cell2-1 to cell2-3 and cell3-1 to 3-3, respectively,as shown in FIG. 2, generality of the invention is not lost. That is,the present invention is applicable to the configuration of FIG. 2 aswell. Here, explanation is made based on the configuration of FIG. 1, asa premise, only for the sake of simplicity. Although the present radiocommunication system has a preferred configuration conforming to thespecifications of LTE, the present invention is not limited to thisconfiguration.

<Exemplary Embodiment 1>

FIGS. 3 to 13 are diagrams illustrating an exemplary embodiment 1 of thepresent invention. It is assumed that, in the first exemplaryembodiment, each of the eNB1, eNB2 has the function of CoMPtransmission/reception, and that the cooperating set (CoMP cooperatingset) is not configured so as to be specific to each radio terminal (UE),but so as to be specific to a cell.

FIG. 3 is a sequential diagram in which the cell1 of the eNB1 and thecell2 of the eNB2 are set in the same cooperating set (CoMP cooperatingset).

The eNB1 instructed the UE1 and the UE2 previously to make measurementreports on the neighbor cells (not shown in the drawing). The UE1 andthe UE2 make measurement reports on the cell2 as a neighbor cell of thecell1.

In case the received quality of the downlink signal of the cell2,reported from the UE 1 and UE2, has met a given condition (for example,is greater than or equal to a given threshold value), a trigger to addthe cell2 to the CoMP cooperating set1 (Trigger to add cell2 to CoMPcooperating set1) is made and the eNB1 thus proceeds to the operation ofadding the cell2 to the cooperating set (CoMP cooperating set).

The eNB1 requests the eNB2 which manages the cell2, to configure thecooperating set (CoMP cooperating set), that is, makes a CoMP setconfiguration request, in preparation for performing CoMPtransmission/reception by cooperation with the eNB1. In the presentembodiment, the eNB1 notifies the eNB2, by the above request message, ofthe control information on CoMP (CoMP control information) that isconfigured in or retained by the base station.

The eNB2 has the function of CoMP transmission/reception, and makes aresponse (CoMP set configuration response) to the request forconfiguring the cooperating set (CoMP cooperating set). In this case,the eNB2 sends ACK (acknowledge response) or the equivalent informationand the control information on CoMP (CoMP control information) to theeNB1 (Request/response Step).

On receiving the ACK from the eNB2, the eNB1 updates (or makes initialconfiguration of) the cooperating set 1 (CoMP cooperating set 1) of theeNB1 (CoMP cooperating set 1 update).

The eNB1 notifies the O&M of the update of the cooperating set 1 (CoMPcooperating set 1), that is, of the new addition of the cell2 (CoMPcooperating set status report (cell2 newly added)).

The O&M updates the information on the cooperating set (CoMP cooperatingset) of the eNB1 and the eNB2 retained by the O&M (CoMP cooperating sets1 and 2 update).

The O&M then transmits to the eNB2 an indication of updating acooperating set 2 (CoMP cooperating set 2) retained by the eNB2 (CoMPcooperating set update indicator).

The eNB2 updates (or makes initial configuration of) the cooperating set2 (CoMP cooperating set 2) (CoMP cooperating set 2 update).

The O&M notifies the eNB1 of the completion of update of the cooperatingset (CoMP cooperating set update complete). The above completes theoperation of making preparations for CoMP transmission/reception.

After completion of the update of the cooperating set (CoMP cooperatingset), the eNB1 and the eNB2 decide on the UE that actually performs CoMPtransmission/reception, and the configuration of thetransmission/reception to perform CoMP transmission/reception.

FIGS. 20A and 20B are diagrams schematically illustrating how thecooperating set (CoMP cooperating set) is updated (changed) inaccordance with the present exemplary embodiment. It is assumed that, ifeach of the eNBs includes three cells, as shown in FIG. 2, thecooperating set (CoMP cooperating set) is subjected to initialconfiguration by the eNB location, as shown for example in FIG. 20A.Note that, in the present exemplary embodiment, the cooperating setconsists of three cells at the maximum.

In the present exemplary embodiment, the initial configuration of FIG.20A in the cooperating set (CoMP cooperating set) is updated, as shownfor example in FIG. 20B, as a more adequate cooperating set (CoMPcooperating set update), by making use of the UE's measurement report.In FIG. 20A, the number #1 of the cooperating set consists of threecells, namely the cell 1-1, cell 3-2 and the cell 3-3 of FIG. 2.However, in FIG. 20B, the number #1 of the cooperating set consists ofthree cells, namely the cell 1-1, cell 2-2 and the cell 3-3.

In the present exemplary embodiment, it is assumed that there is justone cooperating set (CoMP cooperating set). It is however possible thatthere are a plurality of cooperating sets (CoMP cooperating sets) andjust one of them is configured.

It is noted that the role of the O&M in the present exemplary embodimentmay be performed by an MME (Mobility Management Entity)/S-GW (ServingGateway) or any of other network nodes.

In the present exemplary embodiment, a trigger to update the cooperatingset (CoMP cooperating set) is made based on the measurement reporttransmitted from the UE to the eNB. It is however possible to update thecooperating set (CoMP cooperating set) using an X2 setup request as atrigger.

In short, the control information on the CoMP may be added to the X2setup request/response (X2 set up request/response). This is effectivefor a case where default configuration for the cooperating set (CoMPcooperating set) is not made.

The cooperating set (CoMP cooperating set) may also be updated, using,as a trigger, the result of measurement by an eNB of the receivedquality of the signal received from another eNB, as the function of theUE mode implemented in e.g., a base station for home use (home basestation). The UE mode herein means a mode in which a base stationreceives a signal sent thereto from another base station for a certainperiod of time.

The technique of the present invention may be applied without dependencyon how to concretely execute the CoMP transmission/reception. As anexample of actually performing CoMP transmission/reception, there is,for example, a centralized scheduling method in which the eNB1, forexample, performs scheduling for both a UE that stays in the cell1 and aUE that stays in the cell2 managed by the eNB2.

In this case, the eNB1 performs scheduling not only of the UE performingCoMP transmission/reception but also of the UE performing the usualtransmission/reception.

There is also a distributed scheduling in which the eNB1 schedules theUE that stays in the cell1, the eNB2 schedules the UE that stays in thecell2, and the eNB1 and the eNB2 negotiate with each other as to thescheduling of the UE to determine whether or not the CoMPtransmission/reception is able to be performed.

In this case, the scheduling for CoMP transmission/reception of the UEthat stays in the cell 1 is notified from the eNB1 to the eNB2, and theeNB2 determines whether or not the scheduling is acceptable.

In the control information on the CoMP (CoMP control information),transmitted between the radio base stations (eNB1 and eNB2), theinformation on whether or not the function of CoMPtransmission/reception is equipped is the necessary minimum information.

The information on whether or not the function of CoMPtransmission/reception is equipped is the information by which toconfirm whether or not each radio base station (eNB) has the function ofCoMP transmission/reception. It is apparent that the eNB which is atransmission source of the request for configuring the cooperating setbasically has the CoMP transmitting/receiving function. Thus, whenreplying a response, the eNB, which is a transmission destination of theCoMP control information, transmits to the eNB of the transmissionsource the information as to whether or not the replying eNB has theCoMP transmission/reception function.

In the present exemplary embodiment, each of the eNB1 and eNB2 has theCoMP transmission/reception function. Therefore, the eNB2 notifies tothe eNB1 the information (e.g., a flag) indicating that the eNB2 has theCoMP transmission/reception function.

Or, the eNB2 may send an acknowledge response (ACK) to the eNB1 toindicate that the eNB2 has the CoMP transmission/reception function.

In order to more appropriately configure the cooperating set (CoMPcooperating set), such information as

-   -   the information on the CoMP transmission/reception scheme being        supported, or    -   the information on whether or not CoMP may be accepted may be        notified in addition to the information as to whether or not the        CoMP transmission/reception function is equipped.

As regards the CoMP transmission/reception scheme being supported, theeNB1 initially notifies the eNB2 of the CoMP transmission/receptionscheme that the eNB1 supports. In response thereto, the eNB2 notifiesthe eNB1 of the CoMP transmission/reception scheme that the eNB2supports.

Or, the eNB1 may notify the eNB2 of the CoMP transmission/receptionscheme that the eNB1 supports and the eNB2 then notifies to the eNB1whether or not the eNB2 supports respective functions supported by theeNB1.

There may arise such a situation in which radio base stations, eachhaving the CoMP function, but supporting just different CoMPtransmission/reception schemes, are added to the same cooperating set(CoMP cooperating set), resulting in the cooperating set not functioningas intended. Such situation may be avoided by the configuration of thepresent exemplary embodiment.

The information on whether or not CoMP transmission/reception may beaccepted is the information on whether or not the radio base stationthat has received CoMP set configuration request is able to accept suchrequest. A flag, for example, may be used to indicate whether or not theradio base station is able to accept the request.

A timeout value of a timer indicating the prospective time during whichthe request in question is unable to be accepted, or a timer used incase the request in question is unable to be accepted, may be notified.An operation employing a timer may be such a one, shown in FIG. 4, inwhich a radio base station has sent a cooperating set configurationrequest (CoMP set configuration request) and received the timeout valueof a timer causes its timer to be started. After the timer has expired,the radio base station may again carry out the processing of making thecooperating set configuration request.

Another example operation may be such a one in which the radio basestation that received the cooperating set configuration request, (thatset the timer), decides, after the timer expired, whether or not it isable to accept the request again.

-   -   In case the radio base station is able to accept the CoMP        transmission/reception, the radio base station may notify the        radio base station that transmitted the cooperating set        configuration request (CoMP set configuration request) of the        fact that the request may be accepted.    -   In case the radio base station is unable to accept the CoMP        transmission/reception, the radio base station may notify the        radio base station that transmitted the cooperating set        configuration request (CoMP set configuration request) of the        timeout value of the timer or of the re-start of the timer.

As yet another example operation, if the radio base station that hasreceived the request is able to accept the CoMP transmission/receptionbefore the timer times out, it may send a notification that it is ableto accept CoMP transmission/reception without waiting for the expirationof the timer.

In this manner, it is possible to prevent a radio base station as asource of transmission of the cooperating set configuration request fromcontinuing to transmit the request even though the radio base station asa destination of transmission is unable to accept CoMPtransmission/reception. It is thus possible to prevent exchangingwasteful information between radio base stations.

As extensions of the CoMP control information that are exchanged betweendifferent radio base stations and that are needed in order to configuremore appropriately the cooperating set (CoMP cooperating set), there are

-   -   functional information of CoMP transmission/reception;    -   configuration information of the cooperating set (CoMP        cooperating set);    -   access stratum (AS) configuration information, and so forth.

As the functional information of CoMP transmission/reception, there are

-   -   presence/absence of the functions of CoMP        transmission/reception; and    -   a CoMP transmission/reception scheme being supported.

As the configuration information of the cooperating set (CoMPcooperating set), there are

-   -   an identifier of the cooperating set (CoMP cooperating set); and    -   the information of other cells belonging to the same cooperating        set (CoMP cooperating set).

The identifier of the cooperating set is used to show which ofcooperating sets is relevant in case a plurality of the cooperating setshave been configured for a single base station. The information of othercells belonging to the same cooperating set is used to indicate which ofthe other cells cooperates (or likely to cooperate). The above listedconfiguration information may be used in case a plurality of cooperatingsets has been configured in order to select a appropriate one of thesets.

As the access stratum (AS) configuration information, there are

-   -   radio resource management information;    -   terminal measurement configuration information; and    -   scheduler information.

The radio resource management information is the information actuallyneeded to execute CoMP transmission/reception, and may, for example, be

-   -   traffic information; and    -   information as to whether or not CoMP transmission/reception        maybe accepted.

The traffic information is the information for the traffic volume orvalue of each cell. The traffic information may be the traffic amount orits quantized value, per se, or a level determined based on severalpredefined threshold values.

Or, the traffic information may simply be a flag indicating whether thetraffic volume is greater (or smaller) than a given threshold value.

It is noted that the traffic volume may be the number of the activeterminals of each cell, usage rate of the radio resources (for example,usage rate per PRB (Physical Resource Block)), H/W (hardware) usagerate, and load on the network (TNL (Transport Network Layer) Load). Theabove listed traffic information may be used, for example, to determinewith which cell the CoMP transmission/reception is to be performed forimprovement of efficiency.

Or, the estimation may be made of the number of terminals that arecapable or prospectively capable of performing CoMPtransmission/reception and the estimation result may be used todetermine the range of execution of the CoMP transmission/reception(physical locations of terminals, threshold values of the receivedquality of the signal sent to the terminal from the neighbor cell, orthe like).

The terminal measurement configuration information is the informationthat is needed in performing CoMP transmission/reception and that aterminal has to report to a radio base station. The terminal measurementconfiguration information includes:

-   -   a type of measurement information the terminal has to measure;    -   a period of reporting of the measurement information; and    -   event information to which a terminal may refer to in deciding        whether or not the measurement report is to be made.

As the type of the measurement information, there are

-   -   received power of a downlink reference signal (pilot signal)        (RSRP: Reference Signal Received Power);    -   received quality (RSRQ: Reference Signal Received Quality or        CQI: Channel Quality Indicator);    -   information on whether the measurement is for the entire system        bands or for only a specified band;    -   information on whether the measurement is of specified values on        per bands, for the entire system bands; and so forth.

The period of reporting of measurement information may, for example, beonce per 100 msec and, in case there are a plurality of types of themeasurement information, the reporting period may be independentlyconfigured for each of the types of the measurement information.

The event information is the information for events which may prompt aterminal to make measurement reports. The event information may include

-   -   a condition for determination (types of event);    -   a threshold value used in the event;    -   an offset value used in the event; and so forth.

As the event, the following may be used

-   -   an event used for handover or the like already specified in 3GPP        LTE, or    -   another event specifically defined for CoMP.

Among the events used for e.g., handover, there are

-   -   an event A1: The quality of a serving cell has become better        than a given threshold value (Serving cell becomes better than        threshold);    -   an event A2: The quality of a serving cell has become worse than        a given threshold value (Serving cell becomes worse than        threshold);    -   an event A3: The quality of a neighbor cell has become better        than that of a serving cell by a value equal to a given offset        (Neighbor becomes offset better than serving cell);    -   an event A4: The quality of a neighbor cell has become better by        more than a given offset (Neighbor becomes better than        threshold);    -   an event A5: The quality of a serving cell has become worse by        more than a given threshold 1 and the quality of the neighbor        cell has become better by more than a given threshold 2 (Serving        cell becomes worse than threshold 1 and neighbor becomes better        than threshold 2).

A particular event for CoMP may include

-   -   a quality of the serving cell being better than a given        threshold as well as;    -   a quality of the neighbor cell being better than that of the        serving cell added by a value equal to a given offset (positive        or negative); and so forth

The threshold or offset values are exchanged between radio basestations, more precisely, a radio base station that is a source oftransmission of the cooperating set configuration request (CoMP setconfiguration request) notifies a radio base station that is adestination of transmission of threshold or offset values. The radiobase station that is the source of transmission allows (or force) theradio base station that is the destination of transmission to use thethreshold or offset values. It is thus possible to avoid a deviation inthe number of terminals taking part in the CoMP transmission/receptionamong cells in the same cooperating set (CoMP cooperating set). Forexample, if a threshold value for decision in a certain cell A is lowerthan that in another cell B, a decision tends to be given that aterminal that stays in the cell A is more liable to perform CoMP than aterminal that stays in the cell B. Therefore, it may be anticipated thatthe number of terminals taking part in the CoMP transmission/receptionhas a deviation among cells. In the present exemplary embodiment, inwhich the cells share e.g., the event-related information for having theterminals make measurement reports, it is possible to avoid deviation inthe number of terminals taking part in the CoMP transmission/receptionamong cells.

Or, in the present exemplary embodiment, the threshold value or theoffset value may be corrected among radio base stations by taking intoaccount the cell deployment.

Since the radio base stations share the measurement information,obtained by the terminals, the information of the same type may be usedby the cells within the same cooperating set (CoMP cooperating set) todecide whether or not CoMP transmission/reception is to be performed.

The scheduler information is the information for terminal scheduling inthe radio base stations taking part in the CoMP transmission/reception.The scheduler information includes a scheduler policy and a schedulertype. The scheduler policy indicates one of

-   -   a Round-Robin (RR) method;    -   a Proportional Fairness (PF) method; and    -   a Maximum C/I (MAX C/I) method.

The scheduler type indicates whether scheduling is centralizedscheduling or distributed scheduling.

In the case of the centralized scheduling, there is further included theinformation as to which radio base station is to perform the scheduling.

By introducing the sharing of the scheduler information among the radiobase stations, the necessary information may be intensively collected ata suitable location in the case of the centralized scheduling. In thecase of the distributed scheduling, the scheduling may be made betweencells within the same cooperating set (CoMP cooperating set) based onthe same policy.

By the above technique, it is possible with the present exemplaryembodiment to automatically and optimally configure the cooperating set(CoMP cooperating set).

In the above description of the present exemplary embodiment, it isassumed that the control information on CoMP (CoMP control information)has been configured in the base station or retained by the base station.However, the control information may be other information which isdynamically changed.

It is noted that, in FIG. 3, the control information on CoMP (CoMPcontrol information) is transmitted included in a message of thecooperating set configuration request/response (CoMP set configurationrequest/response), only by way of illustration and it is as a matter ofcourse that the embodiment is not limited to this configuration.Initially, a part of the control information on CoMP may be transmittedas cooperating set configuration request/response (CoMP setconfiguration request/response) by way of performing a step oftransmitting the partial CoMP control information. The remaining controlinformation on CoMP (Remaining CoMP control information) may then betransmitted in case the cooperating set configuration request/response(CoMP set configuration response) is an acknowledge response (ACK).

Or, the step of the cooperating set configuration request/response (CoMPset configuration request/response) is initially performed. The controlinformation on CoMP may then be transmitted in case the cooperating setconfiguration response (CoMP set configuration response) is anacknowledge response (ACK).

The control information on CoMP, transmitted by the base station (eNB1),transmitting the cooperating set configuration request (CoMP setconfiguration request), does not have to be the same as the controlinformation on CoMP transmitted by the base station (eNB2) returning aresponse (CoMP set configuration response). It is sufficient that thebase station (eNB1) and the base station (eNB2) send just theinformation needed by the respective destinations of transmission. It isalso possible for the base station (eNB1) transmitting the cooperatingset configuration request (CoMP set configuration request) to transmitjust a request message, in which case the CoMP control information istransmitted just by the base station (eNB2) returning the response (CoMPset configuration response). In this case, the request message from theeNB1 becomes a trigger for the eNB2 to transmit the CoMP controlinformation.

Regarding the processing of FIG. 5, when a radio base station that hastransmitted the cooperating set configuration request (CoMP setconfiguration request), shown in FIG. 4, is notified of a timeout valueof a timer, the radio base station may start its timer. After expirationof the timer, the radio base station may again transmit the cooperatingset configuration request.

If connection (X2) has not been set up between the eNB1 and the eNB2, asshown in FIG. 6, X2 connection is initially set up (X2 setup) beforemaking the cooperating set configuration request (CoMP set configurationrequest). Thereafter, the processing similar to that shown in FIG. 3 or5 is performed.

The information on the cooperating set configuration request (CoMP setconfiguration request) or the CoMP control information may betransmitted simultaneously or multiplexed (piggy backed) with theinformation necessary for normal X2 setup.

The control information on CoMP (CoMP control information) may includedifferent information between an eNB that is a source of transmission ofa cooperating set configuration request (CoMP set configuration request)and another eNB that is a destination of transmission of the acooperating set configuration request. There may further be such a casewhere the eNB that is a source of transmission sends a messageindicating just the cooperating set configuration request, but the eNBthat is a destination of transmission returns a response (ACK) to therequest and the detailed control information on CoMP.

The radio base station which transmitted the cooperating setconfiguration request (CoMP set configuration request) shown in FIG. 4and informed of a timeout value of a timer may then start its timer.After expiration of the timer, the radio base station may again performthe processing of the cooperating set configuration request (request).

Moreover, in case an event of the measurement report for CoMP isprescribed as described above, the terminal location information (forexample, a location information acquisition result by GPS (GlobalPositioning System)), may be added to the measurement report for therelevant event, and the so formed measurement report may then benotified.

If the event is for handover, that is, the event is not that of thereport of measurement specific to CoMP, and the base station has givenan instruction to make notification of the location information, such asby a flag, the terminal may report the location information to the basestation.

The terminal location information may presumably be used for configuring

-   -   a cooperating set (CoMP cooperating set);    -   a CoMP transmission point; or the like.

By using the terminal location information, it is possible, in casethere are a plurality of candidate cooperating sets (CoMP cooperatingsets), to select a appropriate one of the sets. It is moreover possibleto select, from among the cooperating sets (CoMP cooperating sets), aCoMP transmission point that actually performs transmission.

Investigations will now be made into the relationship between the NRT(Neighbor Relation Table) in the ANR (Automatic Neighbor Relation)function provided in 3GPP LTE and the cooperating set (CoMP cooperatingset).

An objective of generating an NRT is to appropriately identify aneighbor cell whose received quality is good among cells other than theserving cell to thereby reduce the handover failure ratio. In the NRT,attributes such as “No Remove”, “No X2” or “No HO” are set on a per cellbasis.

On the other hand, an objective of configuring the cooperating set (CoMPcooperating set) is to identify a neighbor cell, having a good receivedquality among cells other than a serving cell and to improvecharacteristics of a radio link, such as throughput, by executingcooperating transmission/reception, that is, CoMPtransmission/reception, from a plurality of base stations, managing therelevant cell.

There is thus a correlation relationship between the cell added to theNRT and the cell added to the cooperating set (CoMP cooperating set).Thus, by adding the attribute(s) of the cooperating set (CoMPcooperating set) to the NRT, it is thought possible to perform uniformmanagement of the neighbor cell relation.

By way of adding the attribute(s) of the cooperating set (CoMPcooperating set) to the NRT, a check column may simply be added toindicate as to whether or not each cell belongs to the same cooperatingset (CoMP cooperating set), as shown for example in FIG. 8. It is seenthat, in FIG. 8, a column of ‘CoMP’ is provided as an attribute inaddition to attributes of No Remove, No X2 or No HO. Note that a checked(check-marked) cell belongs to the cooperating set (CoMP cooperatingset).

If there are a plurality of cooperating sets (CoMP cooperating sets),serial numbers of the cooperating sets, such as #1, #2 and so forth, maybe appended as identifiers to indicate to which serial number set eachcell belongs.

It is noted that the method of management by appending serial numbers ofthe cooperating sets (CoMP cooperating sets) is effective for a casewhere the configuration of the cooperating set (CoMP cooperating set) ischanged or has to be changed with the lapse of time, as shown in FIGS.10(A) and 10(B).

It is supposed that the radio base station of interest is a radio basestation 1 managing the cells 1-1 to 1-3 and CoMP is for a terminal thatstays in the cell 1-1.

A set #1 of the cooperating sets (CoMP cooperating sets) includes cells1-1, 2-3 and 3-2 (FIG. 10(A)). A set #2 contains cells 1-2, 3-3 and 4-2(FIG. 10(B)).

At a specific time point, the set #1 is configured, and CoMPtransmission/reception for a terminal is performed among cells includedin the set #1.

If, at another specific time point, the set 1 is changed to the set #2,and then CoMP transmission/reception for the terminal is going on, amongcells included in the set #2.

Among the factors that cause the change with time of the configurationof the cooperating set (CoMP cooperating set), there is, for example,the traffic volume or value (Loading) in each cell or in eachcooperating set (CoMP cooperating set).

Thus, to keep loading in the cooperating set (CoMP cooperating set) asuniform as possible, switching control (semi-static switching) of thecooperating set is performed. Such control is desirably executed by O&M,but not limited to O&M, and may be executed by, for example, a specificradio base station.

There are cases wherein, in place of the switching with time, as shownin FIG. 10, a plurality of cooperating sets (CoMP cooperating sets) areconfigured simultaneously, as shown in FIG. 11 (One of the cooperatingsets is selected).

In the example shown in FIG. 11, a specific set is selected out of aplurality of cooperating sets (CoMP cooperating sets), depending on thelocation of the terminal, even in the same cell (cell1-1).

In case the terminal is located at a right edge in the cell1-1, as shownin FIG. 11(A), the set #1 is used. In case the terminal is located at aleft edge in the cell1-1, as shown in FIG. 11(B), the set #2 is used.

By so doing, switching may be made to an optimum cooperating set (CoMPcooperating set) depending on the location of the terminal in the cell,even if the cell is the same cell1-1, thus maximizing the gain by CoMPtransmission/reception.

The information on the terminal location may be one obtained by the GPS,as mentioned previously, or may be determined by the base station fromthe measurement reports for the neighbor cells.

It may be thought that there are cases where addition to the cooperatingset (CoMP cooperating set) may have a meaning different from that in thecase of addition to the neighbor cell list.

An objective of the neighbor cell list is to add a cell, to whichhandover of a terminal is most likely to occur (as long as the number ofthe cells that may be added is not exceeded), with omission as little aspossible. By so doing, terminal movement should be managedappropriately.

On the other hand, in the cooperating set (CoMP cooperating set),handover is not necessarily a matter of concern. For example, such acell for which handover is unlikely to occur, given its particular sitelocation, may be added advantageously to the cooperating set (CoMPcooperating set), if the reception level is of a given level.

It is noted that not only cells of radio base stations connected to thesame MME/S-GW but cells of radio base stations connected to a differentMME/S-GW may be added to the neighbor cell list as described above.

On the other hand, it may be thought that just the cells of the radiobase stations, connected to the same MME/S-GW, may be members of thecooperating set (CoMP cooperating set), from the processing delay pointof view. By so doing, the gain by the CoMP may preferably be maximized.

That is, there is a method in which just cells of radio base stationsconnected to the same MME/S-GW are cells that can be added to the samecooperating set (CoMP cooperating set) and cells except the above cells,that is, cells of radio base stations connected to different MME/S-GW,cannot be added.

By configuring the relationship between the neighbor cell list and thecooperating set (CoMP cooperating set), as the foregoing is taken intoaccount, the cooperating set (CoMP cooperating set) may be configuredmore appropriately.

FIG. 12 is a diagram showing an arrangement of a radio base station(eNB) in the present exemplary embodiment. Referring to FIG. 12, a radiobase station eNB20 includes a receiver 201 connected to an antenna 207,a transmitter 202, similarly connected to the antenna 207, a signalprocessing unit 203, a communication control unit 204 and an interfaceunit 205 with an O&M (OMC) 30. In addition, the radio base stationincludes an interface unit (X2 interface) 206 with other eNBs.

The receiver 201 receives a signal from a terminal and the transmitter202 transmits a signal to the terminal. The signal processing unit 203takes charge of signal processing between the radio base station and theterminal, that between the radio base station and another radio basestation, and that between the radio base station and the O&M 30. Thecommunication control unit 204 controls the signaltransmission/reception between the base station and a terminal, betweenthe base station and other radio base stations and between the basestation and the O&M. It is the communication control unit 204 thatcontrols the transmission/reception of the cooperating set configurationrequest/response with regard to CoMP and the control information onCoMP. It is again the communication control unit 204 that manages thecooperating set (CoMP cooperating set) as held by the radio base station(eNB).

FIG. 13 is a diagram showing an arrangement of the configuration of thecontrol station (O&M) in the present exemplary embodiment. Referring toFIG. 13, the O&M 30 includes a signal processing unit 301, acommunication control unit 302, a base station management unit 303 andan interface unit 304 for interfacing with the base stations. The signalprocessing unit 301 takes charge of signal processing between it and theradio base stations. The communication control unit 302 controls whichsignals are to be sent and received between the O&M 30 and the radiobase stations, while controlling the transmission/reception of the CoMPcontrol information according to the present invention. The base stationmanagement unit 303 manages the configuration information of the basestations the O&M 30 takes charge of, while also managing the informationon the neighbor relation and the information on the cooperating set(CoMP cooperating set).

<Modification of the Exemplary Embodiment 1>

In a modification of the first exemplary embodiment of the presentinvention, it is assumed that eNB1 and eNB3 both have the CoMPtransmission/reception function, while the eNB2 does not have suchfunction. It is also assumed that the result of quality measurements forthe cell2 and cell3 by UE1 and UE2 that stay in the cell1 of the eNB1,and the cell2 is better in quality than the cell3.

FIG. 14 is a diagram showing a sequential operation in case the cell1 ofeNB1 and the cell3 of eNB3 are set in the same cooperating set (CoMPcooperating set).

The eNB1 instructed the UE1 and the UE2 to make measurement reports ofthe neighbor cells, previously (not shown). The UE1 and the UE2 makemeasurement reports on the cells 2 and 3 as neighbor cells for the eNB1.

It is assumed that the received quality of a downlink signal in thecell2, reported by the UE1 and the UE2, is better than that in thecell3, and has met a given condition (for example, is higher than agiven threshold value). In this case, the eNB1 commences its operationto add the cell2 to the cooperating set (CoMP cooperating set) (Triggerto add cell2 to CoMP cooperating set 1).

Initially, the eNB1 transmits to the eNB2 that manages the cell2, thecontrol information for CoMP (CoMP control information) in a message ofthe cooperating set configuration request (CoMP set configurationrequest).

However, the eNB2 does not have the CoMP transmission/receptionfunction. The eNB2 thus transmits a negative acknowledge response (NAKor equivalent information) as a response (CoMP set configurationresponse) to the cooperating set configuration request.

In this case, the eNB1 decides whether or not a cell3, reported to be ofgood quality in addition to the cell2 (for example, next to the cell2),satisfies a given condition. If the cell3 satisfies the given condition,the eNB1 commences its operation to add the cell3 to the cooperating set(CoMP cooperating set) (Trigger to add cell3 to CoMP cooperating set 1).This operation is similar to that for the eNB2.

It is thus initially checked whether or not the eNB3 has the CoMPtransmission/reception function. In case the eNB3 has the CoMPtransmission/reception function, the eNB1 receives the CoMP controlinformation from the eNB3 to update (or performs initial configurationof) the cooperating set (CoMP cooperating set), while also notifying theO&M of the update of the cooperating set (CoMP cooperating set statusreport (cell3 newly added)).

The O&M then instructs the eNB3 to update a cooperating set 3 (CoMPcooperating set 3) (CoMP cooperating set update indication). The eNB3updates or initializes the update cooperating set 3 (CoMP cooperatingset 3) (CoMP cooperating set 3 update).

The O&M notifies the eNB1 of completion of the update of the cooperatingset (CoMP cooperating set) (CoMP cooperating set update complete) andthe operation for making preparations for CoMP transmission/reception iscompleted.

After the completion of update of the cooperating set (CoMP cooperatingset), the eNB1 and the eNB3 determine the UE that actually takes chargeof CoMP transmission/reception and the transmission/receptionconfiguration to perform CoMP transmission/reception.

Here, the control information on CoMP (CoMP control information) isnotified in a message of the cooperating set configuration request (CoMPcooperating set configuration request). It is however also possible toinitially perform the step of communicating just the control informationon CoMP necessary for the cooperating set configuration request/response(CoMP set configuration request/response). In case the cooperating setconfiguration response (CoMP set configuration response) is anacknowledge response (ACK), the remaining necessary portion of thecontrol information on CoMP (CoMP control information) may then becommunicated.

Moreover, the base station (eNB1), transmitting the cooperating setconfiguration request (CoMP set configuration request), may transmitjust the request message, while the control information for CoMP may betransmitted just by the base station that returns a response (CoMP setconfiguration response). In such case, the request message from the eNB1becomes a trigger for the eNB3 to transmit the control information forCoMP.

The radio base station that transmitted the cooperating setconfiguration request (CoMP set configuration request) and that isnotified of the timeout value of the timer may start its timer and,after expiration of the timer, may again perform the processing of thecooperating set configuration request.

<Exemplary Embodiment 2>

It is assumed that, in an exemplary embodiment 2 of the presentinvention, the eNB1 to eNB3 all have the function of CoMPtransmission/reception, and that the cooperating set (CoMP cooperatingset) configured is specific to a cell.

The present embodiment differs from the above mentioned first embodimentin that the configuration (update) of the cooperating set (CoMPcooperating set) is done not via the O&M but through just directinformation exchange between eNBs.

FIG. 15 is a sequence diagram for a case where the cell1 of the eNB1 andthe cell2 of the eNB2 are configured in the same cooperating set (CoMPcooperating set).

Initially, the eNB1 instructs the UE1 and the UE2 to make measurementreports of the neighbor cells, previously (not shown). The UE1 and theUE2 make measurement reports to the eNB1 about the cell2 as respectiveneighbor cells.

In case the received quality of the downlink signals of the cell2,reported from the UE 1 and UE2, has met a given condition, the eNB1notifies the eNB2 of a cooperating set (CoMP cooperating set)configuration request (CoMP set configuration request).

At this time, the notification by eNB1 to eNB2 is made by having thecontrol information on CoMP (CoMP control information) included in theconfiguration request message.

The eNB2 has the CoMP transmission/reception function. Thus, the eNB2notifies to eNB1 an acknowledge response (ACK or the equivalentinformation), with the control information on CoMP (CoMP controlinformation), as a response to a cooperating set (CoMP cooperating set)configuration request (CoMP set configuration response).

On receiving an ACK from the eNB2, the eNB1 updates (or initializes) thenumber #1 (set #1) of the cooperating set 1 (CoMP cooperating set 1)retained by the eNB1.

After transmitting the ACK, the eNB2 also updates (or performs initialsetting of) the number #1 (set #1) of the cooperating set 2 (CoMPcooperating set #2) retained by the eNB2.

The eNB1 notifies the O&M of the identifier of the cooperating set 1(CoMP cooperating set #1), here the number (#1), and of the updateinformation (CoMP cooperating set status report (set# updated)). It isnoted that number #1 is to cover both the cell1 and the cell2. The O&Mupdates the information of the cooperating set number #1 it holds (CoMPcooperating set#1 update).

In this manner, the eNB1 and eNB2 complete update of the cooperating set(CoMP cooperating set), and then decide on the UE that actually takescharge of CoMP transmission/reception and on the transmission/receptionconfiguration to perform CoMP transmission/reception.

The control information on CoMP (CoMP control information) is notifiedincluded in the message of the cooperating set configurationrequest/response (CoMP configuration request/response). It is howeverpossible that no control information is included (or only part of thecontrol information may be included) in the configurationrequest/response, in which the control information on CoMP (or remainingpart of the control information on CoMP) may be notified as a separatemessage. That is, a step of the cooperating set configurationrequest/response (CoMP set configuration request/response) is initiallycarried out. In case the cooperating set configuration response (CoMPset configuration response) is an acknowledge response (ACK), thecommunication of the control information on CoMP may be performed.

It is also possible that the base station eNB1 transmitting thecooperating set configuration request notifies just the request message,and that the control information on CoMP is transmitted by just the basestation eNB2 that returns the response (CoMP set configurationresponse). In this case, the request message from the eNB1 becomes atrigger for the eNB2 to transmit the control information on CoMP.

It is also possible that the radio base station that transmitted thecooperating set configuration request (CoMP set configuration request)shown in FIG. 4 and that has been notified of the timeout value of atimer may start the timer. After expiration of the timer, the radio basestation may again perform the processing of a cooperating setconfiguration request.

The number #1 is notified to the O&M as the identifier of thecooperating set (CoMP cooperating set). However, an identifier may alsobe the information other than the number.

<Third Exemplary Embodiment>

In the third exemplary embodiment of the present invention, it isassumed that the eNB1 to eNB3 all have the function of CoMPtransmission/reception, and that the cooperating set (CoMP cooperatingset) configured is proper to the cell. The present exemplary embodimentdiffers from the first exemplary embodiment in that the controlinformation on CoMP (CoMP control information) is sent from the eNB tothe O&M, and in that the configuration (update) of the cooperating set(CoMP cooperating set) is performed by the O&M. Additionally, thetrigger for communication of the CoMP control information in the presentexample is a request from the O&M (CoMP control information request).

FIG. 16 is a sequence diagram for a case where the cell1 of the eNB1 andthe cell2 of the eNB2 are included in the same cooperating set (CoMPcooperating set).

The eNB1 initially instructs the UE1 and the UE2 previously to makemeasurement reports on the neighbor cells (not shown). The UE1 and theUE2 perform measurement reporting of the cell2 that is a neighbor cellneighboring to the UE1 and the UE2, respectively.

In case the received quality of the downlink signal of the cell2,reported from the UE1 and UE2, satisfies a given condition, the eNB1notifies the O&M of the control information on CoMP (CoMP controlinformation). The CoMP control information is notified enclosed in amessage of the cooperating set (CoMP cooperating set) configurationrequest (CoMP set configuration request). It is noted that theinformation on the radio base station (eNB2) or the cell (cell2), thatbecomes a target, for example, the cell ID or the base station ID (eNBID), is appended to the cooperating set configuration request (CoMP setconfiguration request) transmitted from the eNB1 to the O&M. Or, theidentifier of the cooperating set (CoMP cooperating set) may be appendedto the cooperating set configuration request transmitted from the eNB1to the O&M.

When notified of the cooperating set configuration request (CoMP setconfiguration request), the O&M requests the control information forCoMP (CoMP control information) from the eNB2 that becomes a target(CoMP control information request). The eNB2 notifies the O&M of thecontrol information on CoMP (CoMP control information report).

The O&M sets up the cooperating set (CoMP cooperating set) based on thecontrol information on CoMP (CoMP control information) (CoMP cooperatingset#1 update).

In the present exemplary embodiment, the O&M determines that the cell1of eNB1 and the cell2 of eNB2 are to be added to the same cooperatingset #1 (CoMP cooperating set #1), and notifies the eNB1 and eNB2 of thedetermination. At this time, the serial number (#1), for example, isappended as an identifier of the cooperating set (CoMP cooperating set)(CoMP cooperating set configuration (set#1 updated)).

The eNB1 and the eNB2 update the information on the cooperating sets(CoMP cooperating sets) they have (CoMP cooperating set#1 (set#2),update) and recognize each other as the counterpart of cooperation. Thisallows actually performing CoMP transmission/reception.

The information included in the cooperating set configuration (CoMPcooperating set configuration), the O&M notifies to the eNB1, eNB2, mayinclude:

-   -   the above mentioned information of the cooperating sets (CoMP        cooperating sets) (identifier and cell ID);    -   functional information of CoMP transmission/reception (for        example, the CoMP transmission/reception scheme being        supported);    -   access stratum (AS) configuration information; and so forth.

In the present example, the quality of the cell2 reported by UEsatisfying a given condition becomes a trigger for the eNB1 to transmitthe control information on CoMP. On the other hand, the request from thecontrol station (O&M) becomes a trigger for the eNB2 to transmit thecontrol information on CoMP.

The control information on CoMP (CoMP control information) is notifiedincluded in a message of the cooperating set configurationrequest/response. It is also possible that no control information isincluded in the configuration request/response (or only part of thecontrol information may be included in the configurationrequest/response). In that case, the control information on CoMP (theremaining portion of the control information on CoMP) may be notified asa separate message. That is, the step of the cooperating setconfiguration request/response (CoMP set configuration request/response)is initially performed. In case the cooperating set configurationresponse (CoMP set configuration response) is an acknowledge response(ACK), the control information on CoMP may be communicated.

The O&M, which transmitted the cooperating set configuration request(CoMP set configuration request), shown in FIG. 4, and which is notifiedof the timeout value of the timer, may then start a timer. The O&M mayagain perform the processing of cooperating set configuration requestafter expiration of the timer. The present exemplary embodiment differsfrom the exemplary embodiments 1, 2 in that an entity that actuates thetimer is the O&M.

<Fourth Exemplary Embodiment>

In a fourth embodiment of the present invention, it is assumed that theeNB1 to eNB3 all have the CoMP transmission/reception function, and thatthe CoMP cooperating set configured is proper to each cell. The presentexemplary embodiment differs from the first exemplary embodiment in thatthe control information on CoMP (CoMP control information) is notifiedfrom the eNB to the O&M, and in that the O&M determines the initialconfiguration of the cooperating set (CoMP cooperating set) based on thelocation of the eNB (cell).

FIG. 17 is a sequence diagram for a case where cell1 of the eNB1 andcell2 of the eNB2 are configured in the same cooperating set (CoMPcooperating set).

In an initial state, the eNB2 has not been introduced (started), andjust the eNB1 is connected to the O&M.

Initially, the eNB1, responsive to a request for control information onCoMP from the O&M (CoMP control information request) makes a report onthe control information (CoMP control information report).

It is assumed that, at a certain point in time, the eNB2 is introduced(started). The eNB2 then sets up connection with the network (MME/S-GW)(S1 setup) and notifies the completion of connection to the O&M (setupcompete indication).

The O&M requests the control information on CoMP from eNB2 (CoMP controlinformation request) and the eNB2 makes a report on the controlinformation (CoMP control information report).

The O&M sets up the cooperating set (CoMP cooperating set) based on thecontrol information on CoMP of the eNB1 and the eNB2 (CoMP cooperatingset#1 update).

In the present exemplary embodiment, the O&M determines on addition ofthe cell1 of eNB1 and the cell2 of eNB2 to the same cooperating set(CoMP cooperating set #1) and notifies the eNB1 and eNB2 of thedetermination. At this time, the number (#1), for example, is appendedas an identifier of the cooperating set (CoMP cooperating set) (CoMPcooperating set configuration set #1 updated).

The eNB1 and the eNB2 recognize that they belong to the same cooperatingset (CoMP cooperating set) to perform connection therebetween(connection setup) (X2 setup).

After X2 setup completion, the information of the cooperating set (CoMPcooperating set) held by the eNB1 and eNB2 is updated (CoMP cooperatingset #1 (set #2), update). This allows actually executing CoMPtransmission/reception.

The information included in the cooperating set configuration (CoMPcooperating set configuration), the O&M notifies to the eNB1, eNB2, mayinclude:

-   -   the above mentioned information of the cooperating set (CoMP        cooperating set) (identifier and cell ID); and, in addition,    -   the functional information of CoMP transmission/reception (for        example, the supported CoMP transmission/reception scheme); and    -   the access stratum (AS) configuration information.

The O&M, which transmitted the cooperating set configuration request(CoMP set configuration request), shown in FIG. 4, and which is notifiedof the timeout value of the timer, may then start a timer. The O&M mayagain perform the processing of the cooperating set configurationrequest after expiration of the timer. The present exemplary embodimentdiffers from the exemplary embodiments 1, 2 in that an entity thatactuates the timer is the O&M.

In the previous exemplary embodiment, CoMP transmission/reception isfrom one of a plurality of radio base stations to another (see FIG. 21).However, CoMP transmission/reception may also be via a relay node (RN).The multiple radio base stations that perform CoMPtransmission/reception may be

-   -   combination of one or a plurality of radio base stations and a        relay node; or    -   a plurality of relay nodes,        and they perform CoMP transmission/reception for a single        terminal. In the latter case, the multiple relay nodes may        belong to the same radio base station, given that cells of the        relay nodes are neighboring to one another, or may belong to        different radio base stations.

In these cases, notification or exchange of the control information onCoMP or the information exchange of the cooperating set (CoMPcooperating set) is between eNB and RN or between different RNs. In thiscase, the eNB, which is an upper layer station to the RN, iscorresponding to the other radio base station. The control informationon CoMP may be transmitted with the request for connection setup betweenthe eNB and the RN as a trigger.

In an example shown in FIG. 22A, for example, the eNB1 and RN 1belonging to the eNB1 is performing CoMP transmission/reception for aterminal in a cell of RN1 (cell r1).

In an example shown in FIG. 22B, relay nodes RN 1 and RN 2, belonging tothe same base station eNB1, are performing CoMP transmission/receptionfor one terminal. In this case, the RN 1 and RN 2 may transmit thecontrol information on CoMP via eNB1 or not via eNB1, that is, directly.Or, the eNB1 may hold the control information on CoMP for each of RN 1and RN 2, while the RN 1 and RN 2 respectively perform communicationwith the eNB1. To readily and promptly implement this communication,such a method may be used in which, when each RN has establishedconnection with an eNB as a donor (destination of attachment), thecontrol information on CoMP is communicated.

In an example of FIG. 22C, the relay stations RN 1 and RN 2, that belongto different radio base stations, perform CoMP transmission/receptionfor one terminal. In this case, such a method may be used in which RN 1and RN 2 communicate the control information directly or via eNB1 andeNB2. Or, such a method may be used in which the eNB1 holds the controlinformation on CoMP of RN 1, the eNB2 holds the control information onCoMP of RN 2, and RN 1 acquires the control information on CoMP fromeNB2, while RN2 acquiring the control information on CoMP from eNB1. Ina further method, the eNB1 holds the control information on CoMP of RN2, the eNB2 holds the control information on CoMP of RN 2, and RN 1acquires the control information on CoMP of RN 2 from eNB1, while RN 2acquires the control information on CoMP of RN 1 from eNB2.

In the CoMP transmission/reception, not only the relay nodes but alsoRRH (Remote Radio Head), as a radio unit of the radio base station, or aremote base station RRE (Remote Radio Equipment) may be used.

In the above described exemplary embodiments, the radio communicationsystem is assumed to be 3GPP LTE. However, the present invention is notlimited thereto and may be applied to, for example, 3GPP WCDMA (WidebandCode Division Multiple Access), GSM (Global System for MobileCommunications), or to WiMAX (Worldwide Interoperability for MicrowaveAccess).

The exemplary embodiments or examples may be changed or adjusted withinthe framework of the total of the disclosures of the claims, inclusiveof claims, based on the fundamental technical concept of the invention.Further, variegated combinations or selection of elements disclosedherein may be made within the framework of the claims. That is, thepresent invention may encompass various modifications or correctionsthat may occur to those skilled in the art in accordance with the withinthe gamut of the entire disclosure of the present invention, inclusiveof claim and the technical concept of the present invention.

The invention claimed is:
 1. A radio station comprising: a processorthat is configured to control Coordinated Multi Point (CoMP)transmission cooperating with another radio station; and a transmitterthat is configured to transmit, to the another radio station, CoMPinformation that includes: one or multiple identities of one or multiplecells on which the CoMP transmission is capable of being performed; andinformation regarding one or multiple physical resource blocks of theone or multiple cells on which the CoMP transmission is capable of beingperformed, the one or multiple cells being specific to a cell belongingto the radio station and including a cell belonging to the another radiostation.
 2. The radio station according to claim 1, wherein the CoMPinformation includes information regarding one or multiple physicalresource blocks of the one or multiple cells on which the CoMPtransmission is performed.
 3. The radio station according to claim 1,wherein the CoMP information includes one or multiple identities of theone or multiple cells on which the CoMP transmission is performed. 4.The radio station according to claim 1, wherein the CoMP information istransmitted to the another radio station via an X2 interface.
 5. Theradio station according to claim 1, further comprising: a receiver thatis configured to receive a measurement report of Reference SignalReceived Power(RSRP), wherein the measurement report is used to at leastone of determine or validate the CoMP information.
 6. A radio terminalcomprising: a transceiver configured to perform data communication withat least one of a first radio station and a second radio station,wherein the first radio station comprises: a processor that isconfigured to control Coordinated Multi Point (CoMP) transmissioncooperating with the second radio station; and a transmitter that isconfigured to transmit, to the second radio station, CoMP informationthat includes: one or multiple identities of one or multiple cells onwhich the CoMP transmission is capable of being performed; andinformation regarding one or multiple physical resource blocks of theone or multiple cells on which the CoMP transmission is capable of beingperformed, the one or multiple cells being specific to a cell belongingto the radio station and including a cell belonging to the second radiostation.
 7. The radio terminal according to claim 6, wherein the CoMPinformation includes information regarding one or multiple physicalresource blocks of the one or multiple cells on which the CoMPtransmission is performed.
 8. The radio terminal according to claim 6,wherein the CoMP information includes one or multiple identities of theone or multiple cells on which the CoMP transmission is performed. 9.The radio terminal according to claim 6, wherein the CoMP information istransmitted to the second radio station via an X2 interface.
 10. Theradio terminal according to claim 6: the transceiver is configured totransmit a measurement report of Reference Signal Received Power(RSRP),and the measurement report is used to at least one of determine orvalidate the CoMP information.
 11. A radio communication systemcomprising: a radio terminal; a first radio station and a second radiostation, wherein the first radio station and the second radio stationtake part in data transmission/reception with the radio terminal,wherein the first radio station comprises: a processor that isconfigured to control Coordinated Multi Point (CoMP) transmissioncooperating with the second radio station; and a transmitter that isconfigured to transmit, to the second radio station, CoMP informationthat includes: one or multiple identities of one or multiple cells onwhich the CoMP transmission is capable of being performed; andinformation regarding one or multiple physical resource blocks of theone or multiple cells on which the CoMP transmission is capable of beingperformed, the one or multiple cells being specific to a cell belongingto the radio station and including a cell belonging to the second radiostation.
 12. A method for radio communication, the method comprising:controlling, by a radio station, Coordinated Multi Point (CoMP)transmission cooperating with another radio station; and transmitting,to the another radio station, CoMP information that includes: one ormultiple identities of one or multiple cells on which the CoMPtransmission is capable of being performed; and information regardingone or multiple physical resource blocks of the one or multiple cells onwhich the CoMP transmission is capable of being performed, the one ormultiple cells being specific to a cell belonging to the radio stationand including a cell belonging to the another radio station.
 13. Themethod for radio communication according to claim 12, wherein the CoMPinformation includes information regarding one or multiple physicalresource blocks of the one or multiple cells on which the CoMPtransmission is performed.
 14. The method for radio communicationaccording to claim 12, wherein the CoMP information includes one ormultiple identities of the one or multiple cells on which the CoMPtransmission is performed.
 15. The method for radio communicationaccording to claim 12, wherein the CoMP information is transmitted tothe another radio station via an X2 interface.
 16. The method for radiocommunication according to claim 12, further comprising: receiving ameasurement report of Reference Signal Received Power(RSRP), wherein themeasurement report is used to at least one of determine or validate theCoMP information.
 17. A method for radio communication, the methodcomprising: performing, by a radio terminal, data communication with atleast one of a first radio station and a second radio station;controlling, by the first radio station, Coordinated Multi Point (CoMP)transmission cooperating with the second radio station; andtransmitting, to the second radio station, CoMP information thatincludes: one or multiple identities of one or multiple cells on whichthe CoMP transmission is capable of being performed; and informationregarding one or multiple physical resource blocks of the one ormultiple cells on which the CoMP transmission is capable of beingperformed, the one or multiple cells being specific to a cell belongingto the radio station and including a cell belonging to the second radiostation.
 18. A non-transitory computer-readable recording medium storinga program that causes a processor provided on a radio station to executea process comprising: controlling Coordinated Multi Point (CoMP)transmission cooperating with another radio station; and transmitting,to the another radio station, CoMP information that includes: one ormultiple identities of one or multiple cells on which the CoMPtransmission is capable of being performed; and information regardingone or multiple physical resource blocks of the one or multiple cells onwhich the CoMP transmission is capable of being performed, the one ormultiple cells being specific to a cell belonging to the radio stationand including a cell belonging to the another radio station.
 19. Anon-transitory computer-readable recording medium storing a program thatcauses a processor provided on a radio terminal to execute a processcomprising: performing data communication with at least one of a firstradio station and a second radio station, wherein the first radiostation controls Coordinated Multi Point (CoMP) transmission cooperatingwith the second radio station, and transmits, to the second radiostation, CoMP information that includes: one or multiple identities ofone or multiple cells on which the CoMP transmission is capable of beingperformed; and information regarding one or multiple physical resourceblocks of the one or multiple cells on which the CoMP transmission iscapable of being performed, the one or multiple cells being specific toa cell belonging to the radio station and including a cell belonging tothe second radio station.